The present invention relates to a printed-circuit antenna element which is capacitively coupled to a feedline and which produces linear or circular polarization over a wide frequency band. The printed-circuit element is in the form of a conducting patch printed on a dielectric board; if the element is surrounded by a ground plane printed on the same board, the element forms a slot. The printed-circuit element may be directly radiating or electromagnetically coupled to a radiating element, thus forming electromagnetically coupled patches (EMCP) or slots (EMCS). A plurality of such antennas may be combined to make an antenna array.
Printed-circuit antennas have been used for years as compact radiators. However, they have suffered from a number of deficiencies. For example, they are generally efficient radiators of electromagnetic radiation. However, they typically operate over a narrow bandwidth. Also, complicated techniques for connecting them to the feeding circuit have been required to achieve linear and circular polarization, so that low-cost fabrication of arrays of these elements has been difficult to realize.
Some of the above-mentioned problems have been solved. U.S. Pat. No. 3,803,623 discloses a means for making printed-circuit antennas more efficient radiators of electromagnetic radiation. U.S. Pat. No. 3,987,455 discloses a multiple-element printed-circuit antenna array having a broad operational bandwidth. U.S. Pat. No. 4,067,016 discloses a circularly polarized printed-circuit antenna.
The antennas described in the above-mentioned patents still suffer from several deficiencies. They all treat feeding patches directly connected to a feedline.
U.S. Pat. Nos. 4,125,837, 4,125,838, 4,125,839, and 4,316,194 show printed-circuit antennas in which two feedpoints are employed to achieve circular polarization. Each element of the array has a discontinuity, so that the element has an irregular shape. Consequently, circular polarization at a low axial ratio is achieved. Each element is individually directly coupled via a coaxial feedline.
While the patents mentioned so far have solved a number of problems inherent in printed-circuit antenna technology, other difficulties have been encountered. For example, while circular polarization has been achieved, two feedpoints are required, and the antenna elements must be directly connected to a feedline. U.S. Pat. No. 4,477,813 discloses a printed-circuit antenna system with a nonconductively coupled feedline. However, circular polarization is not achieved.
Copending U.S. application Ser. No. 623,877, now U.S. Pat. No. 4,866,451 filed June 25, 1984 and commonly assigned with the present application, discloses a broadband circular polarization technique for a printed-circuit array antenna. While the invention disclosed in this copending application achieves broadband circular polarization. the use of capacitive coupling between the feedline and feeding patch is not disclosed.
With the advent of certain technologies, e.g. microwave integrated circuits (MIC,) monolithic microwave integrated circuits (MMIC,) and direct broadcast satellites (DBS,) a need for inexpensive, easily-fabricated antennas operating over a wide bandwidth has arisen. This need also exists for antenna designs capable of operating in different frequency bands. While all of the patents discussed have solved some of the technical problems individually, none has yet provided a printed-circuit antenna having all of the features necessary for practical applications in certain technologies.